Is there a way to get a WAN IP address from a phone based on its phone number?

I am trying to develop an android application, through I could share some files or other applications in real time. So I am thinking of trying to set up a B]P2P[/B] connection between 2 phones, for that phones would be requiring IP address of each other. Is there any way by which I can get the IP address
of the other device by just using the phone no.
Could you please post some other suggestions for setting up a P2P connections??